1. Field of the Invention
This invention relates to apparatus for and a method of applying a channel shaped adhesive strip having ribs along each side and an adhesive layer between the ribs to a plastic film. Related applications assigned to the same assignee as this application include the following copending applications: "Adhesive Channel Closure for Flexible Bags", Ser. No. 335,798 filed Dec. 30, 1981; "Laminated Pressure Sensitive Adhesive Systems for Use in Plastic Bags", Ser. No. 335,799 filed Dec. 30, 1981; "Protective Strip for Z-Fold Bag Closure", Ser. No. 335,955 filed Dec. 30, 1981 "Adhesive Bag Closure That Opens Easily By Hand But Resists Opening By Contents", Ser. No. 335,800 filed Dec. 30, 1981; and "Splayed Roll Folder for Adhesive Application", Ser. No. 297,523 filed Aug. 28, 1981, the last three applications being incorporated by reference herein.
2. Brief Description of the Prior Art
Numerous closure arrangements have been proposed and employed for securing plastic bags in a closed condition. Such devices include rubber bands, twist ties, paper or plastic coated lengths of wire which are fastened around the gathered and twisted neck of a plastic bag to secure a closed position. Such devices do not form an integral part of a bag structure, and hence may not be readily accessible when it is desired to effect closure of the bag.
A variety of closures for flexible bags have been developed including the so-called profile closure having at least one pair of mating channels, an example of which may be seen in U.S. Pat. No. Re. 28,969 to Naito which shows the Zip-loc storage bag. U.S. Pat. No. 4,186,786 to Kirkpatrick shows colored channels so that the user may more easily detect complete occlusion of profile bag openings. Difficulties have been experienced by the user in closing these profile types of closures because it is difficult and/or inconvenient to obtain good registration of the two parts of the lock.
The use of pressure sensitive adhesives to close plastic bags is an expedient which is readily accessible and not subject to severe registration problems. Typically, bags are packaged within a dispensing carton in either continuous roll form or individually adjacent to one another. When an exposed and unprotected adhesive strip adjacent the mouth of such bag structures has been employed, the bags had a tendency to stick to one another as to exterior objects, following dispensing of individual bags from the container, thus making it difficult to use the bags. Also, the adhesives employed were necessarily non-aggressive in an attempt to alleviate the bag-sticking problem, but this made the closures insecure.
Bag sticking during storage was solved by the arrangement shown in U.S. Pat. No. 3,990,627 to Olsen (and assigned to the same assignee as this application), in which a Z-fold in the bag protects the adhesive strip during shipment and storage. When the bag is to be used, the Z-fold is pulled out to expose the adhesive. This arrangement has been successfully used, but the release of the adhesive strip from its Z-fold protection is not as easy as may be desired.
A method of making a bag closure comprising perforations may be seen in U.S. Pat. No. 2,899,347 to Kindseth.
Thus, it is an object of the present invention to provide a bag closure by coextruding a channel shaped strip of thermoplastic with a layer of pressure sensitive adhesive between the ribs thereof onto a moving web of plastic film which may be formed into plastic bags.
It is another object of the present invention to maintain a temperature differential between the molten thermoplastic and the moving web so that the molten thermoplastic adheres to the moving web upon contact and thereafter cools to prevent puckering of the moving web.
It is a further object of the present invention to provide an apparatus and a method which quickly and economically applies a channel shaped thermoplastic strip to a polymer film without distortion of the channel or the film, and which also applies a substantially uniform adhesive layer between the ribs of the channel.
These and other objects of the invention will be apparent from the following description.